use just once per day for dawn-to-dark hold. it is important to use the product as directed. fixodent and forget it. >>> if fishing along a secluded tropical reef miles away from another soul sounds like your idea of paradise, then you'll relate to the subjects of our next piece. sharks. hundreds of them. whose presence on a coral reef in the south pacific is an important barometer for measuring the health of our oceans. these creatures are critical in keeping the seas in balance, as jeremy hubbard reports. >> reporter: it is a predator's play ground. some of the most shark infested waters in the world. >> how many sharks are here? maybe 50? this is amazing. >> reporter: these sharks have likely never seen humans before. they live in one of the most remote stretches of the south pacific, where an underwater eden exists. a beautiful, wet wilderness, in peril. >> this used to be a really nice coral forest, with really big coral. but now, most of the corals are very small and most of them are dead and covered by algae. >> reporter: this man, a signist tnd national geographic exp